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From: Billy Tsai <billy_tsai@aspeedtech.com>
To: <jic23@kernel.org>, <lars@metafoo.de>, <pmeerw@pmeerw.net>,
	<robh+dt@kernel.org>, <joel@jms.id.au>, <andrew@aj.id.au>,
	<p.zabel@pengutronix.de>, <linux-iio@vger.kernel.org>,
	<devicetree@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-aspeed@lists.ozlabs.org>, <linux-kernel@vger.kernel.org>
Cc: <BMC-SW@aspeedtech.com>
Subject: [v2 6/8] iio: adc: aspeed: Add compensation phase.
Date: Fri, 23 Jul 2021 16:16:19 +0800	[thread overview]
Message-ID: <20210723081621.29477-7-billy_tsai@aspeedtech.com> (raw)
In-Reply-To: <20210723081621.29477-1-billy_tsai@aspeedtech.com>

This patch adds a compensation phase to improve the accurate of adc
measurement. This is the builtin function though input half of the
reference voltage to get the adc offset.

Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
---
 drivers/iio/adc/aspeed_adc.c | 52 ++++++++++++++++++++++++++++++++++--
 1 file changed, 50 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c
index bb6100228cae..0153b28b83b7 100644
--- a/drivers/iio/adc/aspeed_adc.c
+++ b/drivers/iio/adc/aspeed_adc.c
@@ -61,6 +61,7 @@
  * rate for most user case.
  */
 #define ASPEED_ADC_DEF_SAMPLING_RATE	65000
+#define ASPEED_ADC_MAX_RAW_DATA		GENMASK(9, 0)
 
 enum aspeed_adc_version {
 	aspeed_adc_ast2400,
@@ -84,6 +85,7 @@ struct aspeed_adc_data {
 	struct reset_control	*rst;
 	int			vref;
 	u32			sample_period_ns;
+	int			cv;
 };
 
 #define ASPEED_CHAN(_idx, _data_reg_addr) {			\
@@ -115,6 +117,48 @@ static const struct iio_chan_spec aspeed_adc_iio_channels[] = {
 	ASPEED_CHAN(15, 0x2E),
 };
 
+static int aspeed_adc_compensation(struct platform_device *pdev)
+{
+	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
+	struct aspeed_adc_data *data = iio_priv(indio_dev);
+	u32 index, adc_raw = 0;
+	u32 adc_engine_control_reg_val =
+		readl(data->base + ASPEED_REG_ENGINE_CONTROL);
+	adc_engine_control_reg_val |=
+		(ASPEED_ADC_OPERATION_MODE_NORMAL | ASPEED_ADC_ENGINE_ENABLE);
+
+	/*
+	 * Enable compensating sensing:
+	 * After that, the input voltage of adc will force to half of the reference
+	 * voltage. So the expected reading raw data will become half of the max
+	 * value. We can get compensating value = 0x200 - adc read raw value.
+	 * It is recommended to average at least 10 samples to get a final CV.
+	 */
+	writel(adc_engine_control_reg_val | ASPEED_ADC_CTRL_COMPENSATION |
+		       ASPEED_ADC_CTRL_CHANNEL_ENABLE(0),
+	       data->base + ASPEED_REG_ENGINE_CONTROL);
+	/*
+	 * After enable compensating sensing mode need to wait some time for adc stable
+	 * Experiment result is 1ms.
+	 */
+	mdelay(1);
+
+	for (index = 0; index < 16; index++) {
+		/*
+		 * Waiting for the sampling period ensures that the value acquired
+		 * is fresh each time.
+		 */
+		ndelay(data->sample_period_ns);
+		adc_raw += readw(data->base + aspeed_adc_iio_channels[0].address);
+	}
+	adc_raw >>= 4;
+	data->cv = BIT(ASPEED_RESOLUTION_BITS - 1) - adc_raw;
+	writel(adc_engine_control_reg_val,
+	       data->base + ASPEED_REG_ENGINE_CONTROL);
+	dev_dbg(data->dev, "compensating value = %d\n", data->cv);
+	return 0;
+}
+
 static int aspeed_adc_set_sampling_rate(struct iio_dev *indio_dev, u32 rate)
 {
 	struct aspeed_adc_data *data = iio_priv(indio_dev);
@@ -143,7 +187,11 @@ static int aspeed_adc_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		*val = readw(data->base + chan->address);
+		*val = readw(data->base + chan->address) + data->cv;
+		if (*val < 0)
+			*val = 0;
+		else if (*val >= ASPEED_ADC_MAX_RAW_DATA)
+			*val = ASPEED_ADC_MAX_RAW_DATA;
 		return IIO_VAL_INT;
 
 	case IIO_CHAN_INFO_SCALE:
@@ -347,7 +395,7 @@ static int aspeed_adc_probe(struct platform_device *pdev)
 		if (ret)
 			goto poll_timeout_error;
 	}
-
+	aspeed_adc_compensation(pdev);
 	adc_engine_control_reg_val =
 		readl(data->base + ASPEED_REG_ENGINE_CONTROL);
 	/* Start all channels in normal mode. */
-- 
2.25.1


  parent reply	other threads:[~2021-07-23  8:16 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-23  8:16 [v2 0/8] Add support for ast2600 ADC Billy Tsai
2021-07-23  8:16 ` [v2 1/8] dt-bindings: iio: adc: rename the aspeed adc yaml Billy Tsai
2021-07-23 14:44   ` Jonathan Cameron
2021-07-26  6:53     ` Billy Tsai
2021-07-29 20:31       ` Rob Herring
2021-07-31 17:27         ` Jonathan Cameron
2021-07-23  8:16 ` [v2 2/8] dt-bindings: iio: adc: Binding ast2600 adc Billy Tsai
2021-07-23 14:51   ` Jonathan Cameron
2021-07-26  7:21     ` Billy Tsai
2021-07-23  8:16 ` [v2 3/8] iio: adc: aspeed: completes the bitfield declare Billy Tsai
2021-07-23 14:55   ` Jonathan Cameron
2021-07-23  8:16 ` [v2 4/8] iio: adc: aspeed: Allow driver to support ast2600 Billy Tsai
2021-07-23 15:29   ` Jonathan Cameron
2021-07-23  8:16 ` [v2 5/8] iio: adc: aspeed: Add func to set sampling rate Billy Tsai
2021-07-23 15:37   ` Jonathan Cameron
2021-07-23  8:16 ` Billy Tsai [this message]
2021-07-23 15:44   ` [v2 6/8] iio: adc: aspeed: Add compensation phase Jonathan Cameron
2021-07-23  8:16 ` [v2 7/8] iio: adc: aspeed: Fix the calculate error of clock Billy Tsai
2021-07-23  8:16 ` [v2 8/8] iio: adc: aspeed: Support battery sensing Billy Tsai
2021-07-23 15:56   ` Jonathan Cameron
2021-07-26  6:54     ` Billy Tsai

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